Field which is not required throws 'The field does not match required pattern' error.

Steps:
1. Add Form block.
2. On Fields tab and Single line text.
3. Uncheck required.
4. Add Paragraph text (leave required).
5. Submit & Publish.
6. Enter value only for mandatory field.
7. Try to submit.
Actual: "The field does not match required pattern." error from optional field.
Expected: It's possible to submit w/o error.